Malassezia furfur Promotes Staphylococcus epidermidis Growth by Raising pH in Lipid-Free Environments—A Clue to Seborrheic Dermatitis and Dandruff

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Malassezia furfur Promotes Staphylococcus epidermidis Growth by Raising pH in Lipid-Free Environments—A Clue to Seborrheic Dermatitis and Dandruff

Seborrheic dermatitis (SD) and dandruff affect millions worldwide, causing itchy, flaky skin on the scalp, face, and other oily areas. While two common skin microbes—Malassezia furfur (a yeast) and Staphylococcus epidermidis (a bacterium)—are known to be imbalanced in these conditions, how they interact has long been a mystery. A 2019 study from researchers at the First Hospital of China Medical University and the Key Laboratory of Immunodermatology (Ministry of Health and Education) offers a key insight: under the lipid-poor (low-fat) conditions typical of SD/dandruff skin, M. furfur changes the skin’s pH, creating an environment where S. epidermidis can thrive.

The Players: Normal Skin Microbes Gone Imbalanced

Both M. furfur and S. epidermidis are part of the skin’s “normal flora”—microbes that live on us without causing harm when balanced. But in SD/dandruff, their numbers get out of whack: M. furfur levels rise, and S. epidermidis becomes unusually abundant. Antifungal creams (targeting M. furfur) and antibiotics (targeting S. epidermidis) often improve symptoms, suggesting both play a role in causing SD/dandruff. The question was: How do these two microbes interact to drive the condition?

The Study: Testing Interaction Under Lipid-Free Conditions

SD/dandruff skin has lower levels of surface lipids (fats) than healthy skin—a problem for M. furfur, which needs lipids to grow. The researchers hypothesized that without enough lipids, M. furfur might change the skin’s microenvironment (like pH) in a way that helps S. epidermidis grow. To test this, they:

  1. Grew M. furfur in lipid-free conditions: They used a lipid-free medium (BSCP) to mimic SD/dandruff skin. After 15 hours, they removed the yeast cells and collected the leftover liquid (called M. furfur supernatant, or SMF).
  2. Tested SMF on S. epidermidis: They added different dilutions of SMF to S. epidermidis (using standard lab strains from the American Type Culture Collection) and measured growth with a microplate reader (to track turbidity, a sign of bacterial growth) and flow cytometry (to count bacteria accurately).
  3. Investigated pH: They measured the pH of SMF and the lipid-free medium alone, then adjusted the control medium to match SMF’s pH to see if growth differences disappeared.
  4. Looked at urease: They used a urease activity kit (Sigma) to measure how much urease—an enzyme that breaks down urea into ammonia (raising pH)—M. furfur made in lipid-free vs. lipid-rich conditions. They also used a urease inhibitor (acetohydroxamic acid, AHA) to block the enzyme and see if it stopped pH changes.

The Results: pH Is the Key Driver

The team found three critical things:

  1. SMF boosts S. epidermidis growth: S. epidermidis grew faster in SMF than in the lipid-free medium alone—and the more concentrated the SMF, the bigger the effect (a “dose-dependent” response). Flow cytometry confirmed this: non-diluted SMF made S. epidermidis grow significantly more than the control (F = 45.700, P < 0.001).
  2. SMF has a higher pH: SMF was less acidic (pH 6.2) than the lipid-free medium (pH 5.1). When the researchers adjusted the control medium to match SMF’s pH, S. epidermidis grew the same in both—proving pH was the main factor.
  3. Urease from M. furfur raises pH: M. furfur made far more urease in lipid-free conditions than when lipids were present (t = 67.540, P < 0.001). When they blocked urease with AHA, SMF’s pH didn’t rise—and S. epidermidis stopped growing faster.

What This Means for Seborrheic Dermatitis and Dandruff

This study links three key observations about SD/dandruff:

  • Lipid deficiency: SD/dandruff skin has less oil, which stresses M. furfur.
  • pH shift: M. furfur responds to lipid deficiency by making more urease, which raises pH from ~5 (healthy skin) to ~6 (SD/dandruff skin).
  • Bacterial overgrowth: S. epidermidis grows better at pH 6 than 5—so the pH shift gives it an edge.

Why doesn’t another skin bacterium, Propionibacterium acnes (linked to acne), also overgrow? Two reasons:

  • S. epidermidis has a shorter growth cycle—it multiplies faster, using up nutrients before P. acnes can.
  • S. epidermidis actually inhibits P. acnes growth via fermentation, as shown in previous studies.

Clinical Implications and Next Steps

The findings suggest a new way to think about SD/dandruff: it’s not just about one microbe, but about how two microbes interact when the skin’s environment changes. The researchers speculate that adding lipids back to SD/dandruff skin might help rebalance M. furfur’s urease activity, lower pH, and reduce S. epidermidis overgrowth. However, this needs to be tested in human studies (the current work was done in petri dishes, or “in vitro”).

The Bottom Line

This study helps explain why M. furfur and S. epidermidis are both imbalanced in SD/dandruff: under lipid-poor conditions, M. furfur’s urease raises pH, creating a haven for S. epidermidis. By connecting microbial behavior to the skin’s environment, it brings us one step closer to better treatments for a common, frustrating condition.

The study, “Malassezia furfur Promoting Growth of Staphylococcus epidermidis by Increasing pH When Cultured in a Lipid-Free Environment,” was published in Chinese Medical Journal in 2019 by Yang Han, Yu-Jing Zhang, He-Xiao Wang, Yu-Zhe Sun, Yang Yang, Zheng-Xiu Li, Rui-Qun Qi, and Xing-Hua Gao from the Department of Dermatology, First Hospital of China Medical University, Shenyang, China. Funding came from the “111” Project (No. D18011) and “973” Program (No. 2013CB531604).

doi.org/10.1097/CM9.0000000000000152

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